In the semiconductor industry, substrates are connected to one another permanently or temporarily by so-called bonding processes.
By a bonding process, for example, substrates with different functional units, for example substrates with memory chips and microcontrollers, can be stacked on top of one another. A substrate stack with more complex properties is obtained by the stacking and permanent attachment of multiple substrates with different properties. The thus produced substrate stacks have a thickness of a few hundred micrometers.
The bonding technology, however, can also be used for temporary attachment of a substrate and/or a substrate stack. In this case, a product substrate is attached under pressure and/or temperature by means of an adhesive to a carrier substrate. After the processing of the product substrate, the product substrate is detached again from the carrier substrate.
The greatest problem in the state of the art consists in the alignment and the permanent attachment of multiple extremely thin substrates. The stacking of such thin substrates produces a substrate stack, a so-called “multi-stack.” In order to avoid the difficult and cumbersome handling of thin substrates, the alignment and bonding process is performed on substrates with a defined standard thickness. After a second substrate is bonded to a first substrate, the back-thinning of the second substrate is carried out. By the back-thinning process, a thin substrate is produced from a formerly thick substrate. Optionally, another, third, thick substrate, whose thickness is reduced in another back-thinning process, is to be bonded on this second, back-thinned substrate. Substrate stacks of any functionality can thus be produced by the process that theoretically can be repeated often at will.
One technical problem is that a permanent bond cannot be reversed, so that in the case of a misalignment and/or damage, the entire substrate stack constructed up to that point is unusable. A substrate stack that is comprised of multiple substrates can be worth tens of thousands of Euros.